Geology of the Virginias. 199 



chian coal-field. But in Virginia, Eogers determined forty years 

 ago, that there were two distinct divisions of the Great Con- 

 glomerate, with intervening " seams of coal between these divis- 

 ions." Hence the lower division is now recognized as the floor 

 of only a sub-division of the true coal measures, to which 

 Rogers gave the appropriate designation, " Conglomerate Coal 

 Group." To him belongs the honor of having determined its 

 true status in the Virginia series, and yet it has most probably 

 proved to be far more important, (as developed in the Quinne- 

 mont mines, on New River, and the Blue Stone and the Poca- 

 hontas (Flat Top) mines farther to the southwest), than was an- 

 ticipated by him, when, forty years ago he wrote about it, more 

 as having a prospective than a determined value. 



Above the Conglomerate group Rogers recognizes four sub- 

 divisions, to which, in his table, p. 717, he applies the terms 

 "Lower Coal Group," "Lower Barren Group," " Upper Coal 

 Group," " Upper Barren Group." The first three seem to be 

 covered by Prof. Dana's 14 b, c ; and the last appears to coin- 

 cide with 15. For we find on his geological map the area of 

 the " Upper Barren Group " represented as of Permian age,* 

 and mapped down as bordering on the Ohio river, from the 

 mouth of the Great Kanawha to the vicinity of Wheeling, 

 and covering nearly the whole of two tiers of counties along 

 that margin of the State. 



Middle Secondary, (16-17). — Such is Rogers's designation 

 of the groups of Mesozoic age. The lower portion he regards 

 as embracing the Triassic and Jurassic blending into each 

 other; and hence applies to it the term, " Jurasso-Triassic," 

 (16-17), while for like reason he calls the higher portion " Ju- 

 rasso-Cretaceous," (17-18). Rocks of this age in Virginia are 

 found altogether east of the Blue Ridge, and so far as yet de- 

 termined they rest, not upon rocks of the next preceding age, 

 but upon Archaean beds — usually in trough-like depressions, 

 or perhaps in basins of erosion. The extensive areas covered 

 by these rocks are generally of irregular oval form, and in in- 

 terrupted belts having a general N.E. and S.W. trend, corres- 

 ponding with the usual course of the outcrops of the Archaean 

 beds. The Mesozoic coal field near Richmond forms an ex- 

 ceptional case — its longest axis being north and south, and hence 

 parallel to the corresponding part of the Atlantic coast. 



It is worthy of remark, that the northwest margin of the belt 

 of Mesozoic rocks, north of James River, skirts the southeastern 

 base of a range of ridges running nearly parallel with the Blue 



* Prof. Fontaine, of the Virginia State University, and Prof. White, of the Uni- 

 versity of West Virginia, seem to have established the identity of a number of 

 species of the flora of this group with those of the recognized Permian in other 

 regions, American and foreign. , 



